This invention relates generally to the measurement of various optical properties of a fluid flowing through a flow cell and, more particularly, to an optical interface coupler for coupling the flow cell to an optical absorption analyzer.
It is generally necessary to monitor optical properties, such as turbidity, of fluids used in industrial, laboratory, manufacturing, and other processes. Optical absorption analyzers, such as photometric and spectral analyzers, are commonly used for monitoring fluid flowing or circulating through a flow cell in the process stream. With such analyzers, a beam of light energy, transmitted through the fluid, is compared with a reference light source. Various properties of the fluid, such as turbidity or chemical concentrations, may be determined by this comparison. Examples of optical systems for measuring characteristics of fluids include U.S. Pat. No. 4,637,730 and U.S. Patent application Ser. No. 07/637,807 filed Jan. 7, 1991, both of which are incorporated herein by reference.
By use of fiber optic cables, the optical absorption analyzer may be located remotely from the flow cell. Remote location of the analyzer is particularly beneficial if the fluid to be monitored is hazardous or corrosive. A launch cable transmits light energy from the analyzer to the cell and a return cable transmits the light energy from the cell back to the analyzer. Lenses are typically associated with each cable so that the light energy is properly directed through the fluid stream by the launch cable and properly received by the return cable. Focusing the light through the fluid stream and on the return cable increases the amount of transmitted light collected by the return cable.
In some prior art devices, the light energy is focused by spacing the lenses from their respective cables a distance equal to the focal length of the lens. However, the focal length of a lens is dependent on the wavelength of light passing through the lens. With such lens assemblies, the distance between the lens and cable is fixed; each lens assembly can accommodate only a single wavelength of light energy. Thus, the wavelength of the light source must be known so the proper lens assembly may be selected. Such assemblies are usually expensive because manufacturers must precisely make the assemblies to meet a particular user's needs. Also, if the user changes light source or adds a filter to the light source, the focal length of the lens may change, necessitating a new assembly.
Also, such assemblies are typically sealed. As such, components of the assemblies cannot easily be removed or replaced, which may be necessary if a component fails or a design characteristic changes.